The present invention relates to an optical semiconductor module for use in an optical communication system and a method of manufacturing the optical semiconductor module.
Till now, an optical semiconductor module has been widely used in an optical communication system such as a Local Area Network (LAN), a CATV system. Specifically, the optical semiconductor module comprises a substrate and an optical semiconductor chip mounted on the substrate. In this case, and the optical semiconductor chip generally has an optical element, such as a Laser Diode (LD) array, or a Light Emitting Diode (LED) array, an Avalanche Photo Diode (APD) array. An optical waveguide is formed on the substrate and is optically coupled to the optical element. With this structure, it is possible to transmit an optical beam between the optical semiconductor chip and the optical waveguide. This enables application of such an optical semiconductor module to the optical communication system.
Recent efforts have been made to reduce the size of the optical semiconductor module and to manufacture the optical semiconductor module at a low cost.
In order to satisfy the above-mentioned goal of small size at a low cost, a conventional optical semiconductor module has been proposed which has been small in size and able to be mass-produced. The conventional optical semiconductor module, as will later be described in detail, utilizes a flip-chip interconnection technique on a face-down bonding technique. With this technique, a plurality of first electrodes on the optical semiconductor chip are electrically connected to a plurality of second electrodes on the substrate through a plurality of small solder bumps. According to this technique, precise self-alignment is accomplished between the first and the second electrodes by the solder bumps, because each bump has surface tension, as known in the art. This self-alignment effect results in easy assembly of the optical semiconductor module.
However, in order to take advantage of the aforesaid self-alignment effect, sufficient consideration must be given to the height of each bump. Particularly, necessary that each solder bump have a predetermined height so as to enhance the self-alignment effect. However, even when each solder bump has the predetermined height, the chip would not be positioned in place in a vertical direction. The reason is that the solders irregularly shrink and are varied in height from one another when they are cooled. Further, when the chip is positioned with a poor precision in the vertical direction, the optical element is not flush with the optical waveguide. This results in degradation of transmission characteristics of the optical semiconductor module.